Backside capacitor techniques

ABSTRACT

Some embodiments relate to a semiconductor structure including a semiconductor substrate having a frontside surface and a backside surface. An interconnect structure is disposed over the frontside surface. The interconnect structure includes a plurality of metal lines and vias that operably couple semiconductor transistor devices disposed in or on the frontside surface of the semiconductor substrate to one another. A trench is disposed in the backside surface of the semiconductor substrate. The trench is filled with an inner capacitor electrode, a capacitor dielectric layer overlying the inner capacitor electrode, and an outer capacitor electrode overlying the capacitor dielectric layer.

REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/868,289, filed on Jun. 28, 2019, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

Mobile phones and other mobile devices often rely upon ceramiccapacitors and other passive devices discretely mounted to printedcircuit boards (PCBs) of the mobile devices and electrically coupled tointegrated circuits (ICs) of the mobile devices by the PCBs. However,this uses large amounts of surface area on the PCBs and hence limitsmobile device size and/or mobile device functionality. Further,discretely mounting and electrically coupling the passive devicesincreases manufacturing costs. Accordingly, mobile devices areincreasingly turning to integrated passive devices (IPDs) to reducesize, reduce cost, and increase functionality. An IPD is a collection ofone or more passive devices embedded into a single monolithic device andpackaged as an integrated circuit (IC).

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of asemiconductor structure comprising a backside trench capacitor with ahigh capacitance density.

FIG. 2 illustrates a cross-sectional view of some embodiments of asemiconductor structure comprising a backside trench capacitor with ahigh capacitance density.

FIG. 3 illustrates a cross-sectional view of some embodiments of athree-dimensional IC that includes backside trench capacitors.

FIGS. 4-11 illustrate a series of cross-sectional views thatcollectively illustrate some embodiments of manufacturing asemiconductor structure in accordance with some embodiments of thepresent disclosure.

FIG. 12 illustrates a flow chart depicting some embodiments of methodsin accordance with the present disclosure.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Metal-insulator-metal (MIM) or metal-oxide-metal (MOM) capacitors arecommonly embedded in integrated circuits (ICs) and are used in place ofceramic capacitors to reduce the size of mobile devices, reduce the costof mobile devices, increase the functionality of mobile devices, or anycombination of the foregoing. In some instances, an MIM or MOM capacitoris arranged in an interconnect structure overlying a frontside of asemiconductor substrate. For example, the interconnect structure can bemade up of a number of horizontal metal lines (e.g., wires) stacked overone another and interconnected by vertical vias, wherein theinterconnect structure operably couples semiconductor devices (e.g.,transistors) on the frontside of the semiconductor substrate to oneanother to implement a prefined circuit configuration. The MIM/MOMcapacitor can have its electrodes formed in the interconnect structureover the frontside of the substrate, such that the MIM/MOM capacitor iseasily integrated with the rest of the IC. However, for largecapacitance values, a large area on the IC is generally needed for suchMIM/MOM capacitors. This adds cost to the IC, and is thus in someregards less than an optimal solution.

Various embodiments of the present application are directed towards acapacitor that is formed on a backside of a semiconductor substrate.Thus, semiconductor devices such as transistors are formed on afrontside of the semiconductor substrate, and an interconnect structureis formed over the frontside of the substrate to operably couple thesemiconductor devices to one another. A trench is formed in the backsideof the substrate, and is alternatingly lined with conductive layers anddielectric layers stacked over one another to establish a capacitor inthe trench in the backside of the substrate. By forming the capacitor inthe trench in the backside of the substrate, the impact of the capacitoron the overall area of the IC is limited compared to traditional MIM/MOMcapacitors. Further, a number of these substrates, each including one ormore backside capacitors can be stacked over one another in some casesto form a three-dimensional IC that provides relatively high capacitancevalues in a relatively small footprint.

With reference to FIG. 1, a cross-sectional view of some embodiments ofa semiconductor structure 100 comprising a backside trench capacitor isprovided.

The semiconductor structure 100 includes a semiconductor substrate 102having a frontside surface 102 f and a backside surface 102 b.Semiconductor devices 110, such as transistors, are disposed on thefrontside surface 102 f. The illustrated semiconductor device 110manifests as a transistor that includes first and second source/drainregions 126, 128 that are doped with a first doping conductivity (e.g.,n-type). A body region, which is illustrated as corresponding to a wellregion 130 in FIG. 1, is doped with a second doping conductivity (e.g.,p-type), and separates the first and second source/drain regions 126,128 from one another. The second doping type is opposite the firstdoping type. A gate electrode 132 is disposed over the body region, andis separated from the body region by a gate dielectric 134. Othersemiconductor devices, including active devices such as bipolar junctiontransistors (BJTs) or finFETS for example and/or passive devices such asresistors or diodes for example, could be present on the frontsidesurface 102 f.

A frontside interconnect structure 104 is disposed over the frontsidesurface 102 f. The frontside interconnect structure 104 includes aplurality of frontside metal lines and frontside vias that operablycouple the semiconductor devices 110 to one another.

The frontside interconnect structure 104 comprises a plurality ofconductive layers embedded in dielectric material layers. The dielectricmaterial layers comprise a plurality of interlayer dielectric (ILD)layers 106 a, 106 b, 106 c, that each may comprise a suitable dielectricmaterial. For example, in the present embodiments, the plurality of ILDlayers 106 a, 106 b, 106 c may comprise a low dielectric constant(low-k) material, the material having a constant lower than that ofthermal silicon oxide. In other embodiments, the ILD layers 106 a, 106b, 106 c comprise silicon dioxide or another dielectric material. Thedielectric material may be formed by CVD, HDPCVD, PECVD, combinationsthereof, or other suitable processes. For the purposes of illustration,only three frontside ILD layers are shown in FIG. 1, it being understoodthat any number of frontside ILD layers may be implemented and that thefrontside ILD layers as illustrated are merely exemplary.

The plurality of conductive layers in the frontside interconnectstructure 104 provide interconnections between the various semiconductordevices 110. The plurality of conductive layers comprise metal linesincluding metal one lines 108 a, metal two lines 108 b, and so on to thetop-most metal line 108 c. The plurality of conductive layers furthercomprise contacts 110 a to couple the metal one lines 108 a to thesemiconductor devices 110, and vias 110 b, 110 c to couple adjacentmetal lines (e.g., 108 b and 108 c). The conductive layers of thefrontside interconnect structure 104 may comprise conductive materialssuch as aluminum, aluminum/silicon/copper alloy, titanium, titaniumnitride, tungsten, polysilicon, metal silicide, or combinations thereof,formed by a process including PVD, CVD, combinations thereof, or othersuitable processes. Other manufacturing techniques to form the frontsideinterconnect structure 104 may comprise photolithography processing andetching to pattern the conductive materials for vertical connection (forexample, vias/contacts) and horizontal connection (for example, metallayers). Alternatively, a copper multilayer interconnect may be used toform the metal patterns. The copper interconnect structure may comprisecopper, copper alloy, titanium, titanium nitride, tantalum, tantalumnitride, tungsten, polysilicon, metal silicide, or combinations thereof.The copper interconnect may be formed by damascene technique includingdielectric deposition, etching, deposition and planarization. Thedeposition may comprise sputtering, electroplating, CVD or othersuitable processes.

A trench 112 is disposed in the backside surface 102 b of thesemiconductor substrate 102. The trench 112 is filled with a bottomcapacitor electrode 114, a capacitor dielectric layer 116 overlying thebottom capacitor electrode 114, and an upper capacitor electrode 118overlying the capacitor dielectric layer 116. The capacitor dielectriclayer 116 separates the bottom capacitor electrode 114 and uppercapacitor electrode 118 from one another, thereby establishing one ormore capacitor elements in the region of the semiconductor substratenearest the backside surface 102 b.

In the embodiment of FIG. 1, an innermost surface 112 i of the trench112 is spaced apart from and directly below a bottom extent of the wellregion 130 of the semiconductor device 110 in the semiconductorsubstrate. In some embodiments, a doped region 136 lines the innermostsurface of the trench 112, trench sidewalls, and optionally the backsideof the semiconductor substrate, and can act as another capacitorelectrode. Thus, in FIG. 1, a first capacitor element 101 can includethe doped region 136 and the bottom capacitor electrode 114 spaced apartby an inner portion of capacitor dielectric layer 116, and a secondcapacitor element 103 can include the bottom capacitor electrode 114 andthe upper capacitor electrode 118 spaced apart by an outer portion ofthe capacitor dielectric layer 116. In some embodiments, the firstcapacitor element 101 can be arranged in parallel with the secondcapacitor element 103 to realize further increases in capacitance perunit area.

A backside interconnect structure 120 includes a plurality of backsidemetal lines and backside contacts/vias that operably couple the bottomcapacitor electrode 114 and upper capacitor electrode 118 tosemiconductor devices 110 and/or to other backside trench capacitors. Insome embodiments, the backside metal lines are thicker than thefrontside metal lines, however in other embodiments the backside metallines are the same thickness as the frontside metal lines. Thisconfiguration provides a relatively high density capacitance in arelatively small area of the IC.

The backside interconnect structure 120 comprises a plurality ofbackside conductive layers embedded in backside dielectric materiallayers. The dielectric material layers comprise a plurality of backsideILD layers 142 a, 142 b, that each may comprise a suitable dielectricmaterial. For example, in the present embodiments, the plurality ofbackside ILD layers 142 a, 142 b may comprise a low dielectric constant(low-k) material, the material having a constant lower than that ofthermal silicon oxide. In other embodiments, the backside ILD layers 142a, 142 b comprises silicon dioxide or another dielectric material. Thedielectric material may be formed by CVD, HDPCVD, PECVD, combinationsthereof, or other suitable processes. For the purposes of illustration,only two backside ILD layers are shown in the backside interconnectstructure 120 of FIG. 1, it being understood that any number of backsideILD layers may be implemented and that the backside ILD layers asillustrated are merely exemplary.

The plurality of conductive layers in the backside interconnectstructure 120 provide interconnections between the various capacitorelectrodes. The plurality of conductive layers comprise metal linesincluding metal one lines 122 a and a top-most metal line 122 b. Theplurality of conductive layers further comprise contacts 124 to couplethe metal lines to the capacitor electrodes. The conductive layers ofthe backside interconnect structure 120 may comprise conductivematerials such as aluminum, aluminum/silicon/copper alloy, titanium,titanium nitride, tungsten, polysilicon, metal silicide, or combinationsthereof, formed by a process including PVD, CVD, combinations thereof,or other suitable. Other manufacturing techniques to form the backsideinterconnect structure 120 may comprise photolithography processing andetching to pattern the conductive materials for vertical connection (forexample, vias/contacts) and horizontal connection (for example, metallayers). Alternatively, a copper multilayer interconnect may be used toform the metal patterns. The copper interconnect structure may comprisecopper, copper alloy, titanium, titanium nitride, tantalum, tantalumnitride, tungsten, polysilicon, metal silicide, or combinations thereof.The copper interconnect may be formed by damascene technique includingdielectric deposition, etching, deposition and planarization. Thedeposition may comprise sputtering, electroplating, CVD or othersuitable processes.

FIG. 2 illustrates another embodiment, wherein the innermost surface 112i of the trench 112 is laterally offset from and has a vertical overlapwith the well region 130 of the semiconductor device 110 in thesemiconductor substrate. Further, FIG. 2 illustrates an example wherethe backside trench capacitor includes a bottom capacitor electrode 114and an intermediate capacitor electrode 117, which are separated fromone another by a lower portion of the capacitor dielectric 116 a; and anupper capacitor electrode 118 which is separated from the intermediatecapacitor electrode 117 by an upper portion of the capacitor dielectriclayer 116 b. In some embodiments, a doped region 136 lines the innermostsurface of the trench 112, trench sidewalls, and optionally the backsideof the semiconductor substrate, and can act as another capacitorelectrode. Thus, in FIG. 2, a first capacitor element 101 can includethe doped region 136 and the bottom capacitor electrode 114, which arespaced apart by a bottom portion of the capacitor dielectric layer 116c. A second capacitor element 103 can include the bottom capacitorelectrode 114 and the intermediate capacitor electrode 117, which arespaced apart by the lower portion of the capacitor dielectric layer 116a. A third capacitor element 105 can include the intermediate capacitorelectrode 117 and the upper capacitor electrode 118, which are spacedapart by the upper portion of the capacitor dielectric layer 116 b. Insome embodiments, the first capacitor element 101 can be arranged inparallel with the second capacitor element 103 and/or the thirdcapacitor element 105 to realize further increases in capacitance perunit area. Whereas the upper capacitor electrode 118 of FIG. 1 was asolid body, the upper capacitor electrode 118 of FIG. 2 is U-shaped incross-section. In the example of FIG. 2, the bottom capacitor electrode114 and/or intermediate capacitor electrode 117 have upper surfaces thatare below an upper surface of the metal one line 122 a, and the uppersurface of the upper capacitor electrode 118 can be level or planar withthe upper surface of the metal one line 122 a in some embodiments.

It will be appreciated that although FIG. 1 and FIG. 2 are illustratedas examples, these illustrated embodiments are non-limiting. Forexample, though FIG. 1 shows two conductive layers disposed over aninnermost surface of the trench, and FIG. 2 shows three conductivelayers disposed over an innermost surface of the trench, any number ofconductive layers could be present. Generally, adding additionalconductive layers will tend to further increase the capacitance when thecorresponding capacitor electrodes are coupled in parallel. However,these additional layers also add to processing time and complexity, sohaving fewer conductive layers as in FIG. 1 provides a stream-linedapproach.

With reference to FIG. 3, a cross-sectional view of some embodiments ofa semiconductor structure 300 is provided. The semiconductor structure300 includes a number of substrates stacked over one another, with oneor more of the substrates including at least one backside trenchcapacitor.

The semiconductor structure 300 includes a first semiconductor substrate302 having a first frontside surface 302 f and a first backside surface302 b. A second semiconductor substrate 304 has a second frontsidesurface 304 f and a second backside surface 304 b. The secondsemiconductor substrate 304 is disposed over the first semiconductorsubstrate 302. A first interconnect structure 306 is disposed betweenthe first frontside surface 302 f of the first semiconductor substrate302 and the second frontside surface 304 f of the second semiconductorsubstrate 304. The first interconnect structure 306 includes a firstplurality of metal lines and vias that operably couple firstsemiconductor devices disposed in or on the first frontside surface 302f of the first semiconductor substrate 302 to one another. A secondinterconnect structure 312 is disposed between the first interconnectstructure 306 and the second frontside surface 304 f of the secondsemiconductor substrate 304. The second interconnect structure 312includes a second plurality of metal lines and vias that operably couplesecond semiconductor devices disposed in or on the second frontsidesurface 304 f of the second semiconductor substrate 304 to one another.A first trench 317 is disposed in the first backside surface 302 b ofthe first semiconductor substrate 302. The first trench 317 is filledwith a first inner capacitor electrode 314, a first capacitor dielectriclayer 316 overlying the first inner capacitor electrode 314, and a firstouter capacitor electrode 318 overlying the first capacitor dielectriclayer 316. Thus, for example, the capacitor in FIG. 1 and/or FIG. 2 canbe inset into the first trench 317 of FIG. 3 in some embodiments. Asecond trench 319 is disposed in the second backside surface of thesecond semiconductor substrate 304. The second trench 319 is filled witha second inner capacitor electrode 344, a second capacitor dielectriclayer 346 overlying the second inner capacitor electrode, and a secondouter capacitor electrode 348 overlying the second capacitor dielectriclayer. Thus, for example, the capacitor in FIG. 1 and/or FIG. 2 can beinset into the second trench 319 of FIG. 3 in some embodiments.

The semiconductor structure 300 further includes a third semiconductorsubstrate 320 having a third frontside surface 320 f and a thirdbackside surface 320 b. The third semiconductor substrate 320 isdisposed beneath the first semiconductor substrate 302. A thirdinterconnect structure 322 is disposed between the first backsidesurface 302 b of the first semiconductor substrate and the thirdfrontside surface 320 f of the third semiconductor substrate. The thirdinterconnect structure 322 includes a third plurality of metal lines andvias that operably couple third semiconductor devices disposed in or onthe third frontside surface of the third semiconductor substrate to oneanother. A third trench 326 is disposed in the third backside surface ofthe third semiconductor substrate. The third trench 326 is filled with athird inner capacitor electrode 354, a third capacitor dielectric layer356 overlying the third inner capacitor electrode, and a third outercapacitor electrode 358 overlying the third capacitor dielectric layer.Thus, for example, the capacitor in FIG. 1 and/or FIG. 2 can be insetinto the third trench 326 of FIG. 3 in some embodiments.

The semiconductor structure 300 further includes: a fourth semiconductorsubstrate 328 having a fourth frontside surface 328 f and a fourthbackside surface 328 b. The fourth semiconductor substrate 328 isdisposed beneath the third semiconductor substrate 320. A fourthinterconnect structure 330 is disposed between the third backsidesurface of the third semiconductor substrate 320 and the fourthfrontside surface of the fourth semiconductor substrate 328. The fourthinterconnect structure 330 includes a fourth plurality of metal linesand vias that operably couple fourth semiconductor devices disposed inor on the fourth frontside surface of the fourth semiconductor substrate328 to one another. The fourth semiconductor substrate 328 has a fourththickness that is greater than a first thickness of the firstsemiconductor substrate 302. Additional substrates (e.g. 350) can alsobe present in some instances, and can also include additional backsidetrench capacitors (e.g., 370).

A bond pad or landing pad 372, which comprises a metal such as copper oraluminum for example, is disposed over a passivation layer 374, and iscoupled to a second backside interconnect structure 308 via aredistribution layer (RDL) via 376. The bonding pad or landing pad 372can be operably coupled to one or more capacitors or semiconductordevices on the 3DIC through the RDL via 376 and second backsideinterconnect structure 308. The passivation layer 374 can comprise aresin, an epoxy, a plastic, or a ceramic material for example.

In some embodiments, each of the first, second, and third semiconductorsubstrates have a first thickness that is equal for each of the first,second, and third semiconductor substrates, and the fourth semiconductorsubstrate 328 has a fourth thickness that is greater than the firstthickness.

The semiconductor structure 300 further includes through substrate vias(TSV) extending through the various substrates. For example, the firstsemiconductor substrate 302 includes a TSV 340 to couple the firstinterconnect structure 306 to the third interconnect structure 322. Thethrough substrate vias have outer sidewalls which are spaced apart by afirst distance on the first frontside and which are spaced apart by asecond distance on the first backside, the first distance being lessthan the second distance. The other semiconductor substrates can alsoinclude through substrate vias, with through substrate vias being absentfrom the lowermost substrate (e.g., fourth semiconductor substrate 328)in some embodiments.

The semiconductor structure 300 further includes various bondingstructures to bond the various substrates and interconnect structures toone another. For example, a first frontside bonding structure 342disposed on the first frontside of the first semiconductor substrate 302is bonded to a second frontside bonding structure 345 disposed over thesecond semiconductor substrate 304. The first frontside bondingstructure 342 corresponds to the second frontside bonding structure 345and is bonded to the second frontside bonding structure through a hybridbond. In some embodiments, the first frontside bonding structure 342includes conductive features (e.g., metal features 343) disposed in afield of a dielectric layer 347, and the second frontside bondingstructure 345 includes conductive features (e.g., metal features 351)disposed in a field of a dielectric layer 349. Further, some features381 of the first frontside bonding structure 342 may be electricallycoupled to semiconductor devices and/or capacitors on the firstsemiconductor substrate 302, while other features are “dummy” structures382 that aid in bonding but which are electrically floating ordisconnected from semiconductor devices and capacitors on thesubstrates.

The semiconductor substrate(s) 302, 304, 320, 328, and/or 350 may be orcomprise, for example, a bulk semiconductor substrate, a SOI substrate,or some other semiconductor substrate. Further, the semiconductorsubstrate(s) may be or comprise, for example, monocrystalline silicon,some other silicon, or some other semiconductor material.

The capacitor dielectric layers 316, 346 are made of or comprise silicondioxide, a high κ dielectric material, or a low-K dielectric material insome embodiments. Use of a high κ dielectric material is advantageous inthat it increases the capacitance of the capacitor for a given areacompared to silicon dioxide or a low-K dielectric material. The metalinterconnect lines and/or vias typically are made of or comprise ametal, such as aluminum and/or copper for example.

In some embodiments, the semiconductor structure 300 of FIG. 3 is formedby forming semiconductor transistor devices, a frontside interconnectstructure, a backside capacitor structure, and a backside interconnectstructure for the first semiconductor substrate (optionally, thesemiconductor substrate can be thinned, for example, by using a grindingstep prior to formation of the trench in the backside of the substrate,in which case the backside capacitor may more closely resemble that ofFIG. 2 than that of FIG. 1). Semiconductor transistor devices, afrontside interconnect structure, a backside capacitor structure, and abackside interconnect structure can also be formed for the othersemiconductor substrates. The frontside interconnect structure of onesubstrate can then be bonded, for example by using a hybrid bond, toeither a frontside interconnect structure or backside interconnectstructure of another substrate. The substrates can be stacked in thismanner to form the structure of FIG. 3.

FIGS. 4-12 illustrate a series of cross-sectional views thatcollectively illustrate some embodiments of manufacturing asemiconductor structure in accordance with some embodiments of thepresent disclosure.

In FIG. 4, a first semiconductor substrate 102 is provided, and aplurality of semiconductor devices 110, such as transistors are formedon a first frontside 102 f of the first semiconductor substrate 102. Insome embodiments, the first semiconductor substrate 102 can comprise amonocrystalline silicon wafer, a semiconductor on insulator (SOI) wafer,or another semiconductor substrate. A first frontside interconnectstructure 104 is formed over the first frontside of the first substrate,and a through-substrate-via (TSV) 186 is also formed. In someembodiments, the TSV 186 can be formed before the semiconductor devices110, but in other embodiments, the TSV 186 can be formed after thesemiconductor devices 110. Often, the TSV 186 comprises copper or acopper alloy, and can have sidewalls that are lined with a barrier layercomprising tantalum or titanium for example.

In FIG. 5, a first trench 112 is formed in a backside of the firstsemiconductor substrate 102. The first trench 112 may be formed byspinning a photoresist solution on the backside of the firstsemiconductor substrate 102, baking the photoresist, then exposing thephotoresist to light through a reticle or photomask, and developing theexposed photoresist to form a patterned mask on the backside of thefirst substrate. Then, with the patterned mask in place, an etch iscarried out. The etch can be a wet etch or dry etch, and if a highaspect ratio trench is desired, a Bosch etching process can be used insome implementations. In other embodiments, extreme ultra-violet (UV)photolithography and/or electron beam lithography techniques could beused to form the first trench 112, among others.

In FIG. 6, a first dielectric layer 116 a, such as a high-k dielectriclayer is formed over the backside of the first semiconductor substrate102, including on an innermost surface and sidewalls of the trench 112.The first dielectric layer 116 a can be formed by physical vapordeposition (PVD), chemical vapor deposition (CVD), atomic layerdeposition (ALD), or thermal oxidation, or others. In some embodiments,the first dielectric layer 116 a is a conformal layer. In someembodiments, the first dielectric layer 116 a is a high-k dielectric andcan comprise hafnium and/or zirconium, and can take the form of hafniumsilicate, zirconium silicate, hafnium dioxide and/or zirconium dioxide,among others.

Still referring to FIG. 6, a first conductive layer 114 is then formedover the first dielectric layer 116 a. The first conductive layer 114can correspond to a capacitor electrode, and can comprise a metal ordoped polysilicon and can be conformal. For example, metals can includecopper, aluminum, tungsten, nickel, titanium, zirconium and/or others;and can be formed by PVD, CVD, ALD, sputtering, or electroplating, amongothers.

In FIG. 7, the first conducive layer 114 has been patterned, forexample, by forming a photomask and then performing an etch with thephotomask in place. The photomask is then removed, for example by ashingor plasma stripping, and a second dielectric layer 116 b, such as ahigh-k dielectric layer is formed over an upper surface of the firstconductive layer 114 in the trench 112. The second dielectric layer 116b lines an innermost surface and sidewalls of the trench, lines innersidewalls of the first conductive layer in the trench, and extends overan upper surface of the first conductive layer 114 and first dielectriclayer 116 a on the backside of the substrate out of the trench. In someembodiments, the second dielectric layer 116 b is a conformal layer. Thesecond dielectric layer 116 b can be formed by PVD, CVD, ALD, or thermaloxidation, or others. In some embodiments, the second dielectric layer116 b can comprise a high-k dielectric material comprising hafniumand/or zirconium, and can take the form of hafnium silicate, zirconiumsilicate, hafnium dioxide and/or zirconium dioxide, among others.

Still referring to FIG. 7, a second conductive layer 118 is then formedover the second dielectric layer 116 b. The second conductive layer 118can correspond to a capacitor electrode, and can comprise a metal ordoped polysilicon. For example, metals can include copper, aluminum,tungsten, nickel, titanium, zirconium and/or others; and can be formedby PVD, CVD, ALD, sputtering, or electroplating, among others.

In FIG. 8, a chemical mechanical planarization (CMP) operation isperformed. In the illustrated embodiments, the CMP operation planarizesan upper surface of the first conductive layer 114 with an upper surfaceof the second conductive layer 118. It will be appreciated that in otherembodiments, for example where additional capacitor dielectric layersand/or additional conductive layers are present, the CMP operation maystop on one or more of the conductive layers and/or capacitor dielectriclayers while leaving other of the these layers at different stepheights.

In FIG. 9, a first backside interconnect structure 120 is formed. Thefirst backside interconnect structure 120 can be formed, for example, byforming a first ILD layer over the planarized upper surface of FIG. 8,and then using photolithography to form contact openings in the firstILD layer. Metal, which can comprise tungsten, aluminum, and/or copperfor example, can be formed in the contact openings, and can then beplanarized to establish contacts. Additional ILD layers can be formed,and then via openings and line openings can be formed and filled withmetal, such as copper or copper-aluminum alloy, and then can then beplanarized to form metal lines and vias of the first backsideinterconnect structure.

In FIG. 10, the first semiconductor structure 100 (which includes thefirst semiconductor substrate 102, the first frontside interconnectstructure 104 disposed on a frontside of the first semiconductorsubstrate 102, and the first backside interconnect structure 120disposed on the backside of the first semiconductor substrate 102) isbonded to a second semiconductor structure 200 (which includes a secondsemiconductor substrate 202, a second frontside interconnect structure204 and a second backside interconnect structure 220). The bondingprocess is a hybrid bonding process, whereby dielectric material of thefirst semiconductor structure 100 is bonded to dielectric material ofthe second semiconductor structure 200; and whereby metal of the firstsemiconductor structure 100 is bonded to metal of the secondsemiconductor structure 200.

In FIG. 11, additional semiconductor structures, including a thirdsemiconductor structure 300, fourth semiconductor structure 400, andfifth semiconductor structure 500, are bonded together to form athree-dimensional IC 1100. Typically, these additional semiconductorstructures are bonded together using a bonding structure, which caninclude a hybrid bond or can include solder balls, solder bumps,conductive pillars such as copper or copper-alloy pillars, microbumps,or other bonding structures.

For example, a third semiconductor substrate 303 having a thirdfrontside surface 303 f and a third backside surface 303 b can be bondedto a first backside interconnect structure 120. A third trench 326 isdisposed in the third backside surface of the third semiconductorsubstrate 302. The third trench 326 is filled with a third innercapacitor electrode, a third capacitor dielectric layer overlying thethird inner capacitor electrode, and a third outer capacitor electrodeoverlying the third capacitor dielectric layer. Thus, for example, thecapacitor in FIG. 1 and/or FIG. 2 can be inset into the third trench 326in some embodiments. Thus, after bonding, the third semiconductorsubstrate 303 is disposed beneath the first semiconductor substrate 102.The first backside interconnect structure 120 and a third frontsideinterconnect structure 305 are disposed between the first backsidesurface 102 b of the first semiconductor substrate and the thirdfrontside surface 303 f of the third semiconductor substrate. The firstbackside interconnect structure 120 includes a plurality of metal linesand vias that are operably coupled to capacitor electrodes of the firsttrench capacitor to other conductive features in the 3DIC. The thirdfrontside interconnect structure 305 also includes a plurality of metallines and vias that operably couple semiconductor devices disposed in oron the third substrate to one another.

A fourth semiconductor substrate 402 having a fourth frontside surface402 f and a fourth backside surface 402 b, and a fifth semiconductorsubstrate 502 having a fifth frontside surface 502 f and fifth backsidesurface 502 b can also be bonded as part of the 3DIC 1100. A fourthfrontside interconnect structure 404 is present. A fifth frontsideinterconnect structure 504 and a fifth backside interconnect structure520 are also present. The fifth frontside interconnect structure 504 isbonded to the third backside interconnect structure 321, and the fifthbackside interconnect structure 520 is bonded to the fourth frontsideinterconnect structure 404.

FIG. 12 shows some embodiments of a method for forming a semiconductorstructure in accordance with some aspects of the disclosure. It will beappreciated that the illustrated acts can be performed in differentorders in other embodiments, one or more of the illustrated acts may beomitted in some other embodiments, and additional acts that are notillustrated in FIG. 12 may be present in other implementations. Thus,FIG. 12 is merely a non-limiting example.

In 1202, semiconductor devices are formed on a frontside of asemiconductor substrate.

In 1204, a trench is formed in a backside of the semiconductorsubstrate.

In 1206, alternating conductive and insulating layers are formed in thetrench on the backside of the semiconductor substrate to establish abackside capacitor.

In 1208, a backside interconnect structure is formed on the backside ofthe semiconductor substrate to couple to capacitor electrodes of thebackside capacitor.

In 1210, the semiconductor substrate and is optionally bonded to othersemiconductor substrates to form a 3DIC.

Thus, some embodiments of the present disclosure relate to asemiconductor structure. The structure includes a semiconductorsubstrate having a frontside surface and a backside surface. A frontsideinterconnect structure is disposed over the frontside surface, andincludes a plurality of metal lines and vias that operably couplesemiconductor devices disposed in or on the frontside surface of thesemiconductor substrate to one another. A trench is disposed in thebackside surface of the semiconductor substrate. The trench is filledwith an inner capacitor electrode in the trench, a capacitor dielectriclayer in the trench and overlying the inner capacitor electrode, and anouter capacitor electrode in the trench and overlying the capacitordielectric layer.

Other embodiments relate to a semiconductor structure. The semiconductorstructure includes a first semiconductor substrate having a firstfrontside surface and a first backside surface. A second semiconductorsubstrate has a second frontside surface and a second backside surface.The second semiconductor substrate is disposed over the firstsemiconductor substrate. A first interconnect structure is disposedbetween the first frontside surface of the first semiconductor substrateand the second frontside surface of the second semiconductor substrate.The first interconnect structure includes a first plurality of metallines and vias that operably couple first semiconductor devices disposedin or on the first frontside surface of the first semiconductorsubstrate to one another. A second interconnect structure is disposedbetween the first interconnect structure and the second frontsidesurface of the second semiconductor substrate. The second interconnectstructure includes a second plurality of metal lines and vias thatoperably couple second semiconductor devices disposed in or on thesecond frontside surface of the second semiconductor substrate to oneanother. A first trench is disposed in the first backside surface of thefirst semiconductor substrate. The first trench is filled with a firstinner capacitor electrode, a first capacitor dielectric layer overlyingthe first inner capacitor electrode, and a first outer capacitorelectrode overlying the first capacitor dielectric layer. A secondtrench is disposed in the second backside surface of the secondsemiconductor substrate. The second trench is filled with a second innercapacitor electrode, a second capacitor dielectric layer overlying thesecond inner capacitor electrode, and a second outer capacitor electrodeoverlying the second capacitor dielectric layer.

Some other embodiments relate to a method. In the method, semiconductordevices are formed on a frontside of a semiconductor substrate. A trenchis formed in a backside of the semiconductor substrate. Conductive andinsulating layers are alternatingly formed in the trench on the backsideof the semiconductor substrate to establish a backside capacitor. Abackside interconnect structure is formed on the backside of thesemiconductor substrate to couple to capacitor electrodes of thebackside capacitor.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor structure comprising: asemiconductor substrate having an overall thickness defined between afrontside surface and a backside surface; a well region corresponding toa semiconductor device and extending from the frontside surface to adepth into the semiconductor substrate, a frontside interconnectstructure disposed over the frontside surface, the frontsideinterconnect structure including a plurality of metal lines and viasthat operably couple semiconductor devices disposed in or on thefrontside surface of the semiconductor substrate to one another; and atrench disposed in the backside surface of the semiconductor substrate,the trench being filled with an inner capacitor electrode in the trench,a capacitor dielectric layer in the trench and overlying the innercapacitor electrode, and an outer capacitor electrode in the trench andoverlying the capacitor dielectric layer; wherein the semiconductorsubstrate has a reduced thickness as measured from a bottom surface ofthe trench to the frontside surface, and the reduced thickness beingless than the overall thickness and being less than the depth of thewell region.
 2. The semiconductor structure of claim 1, wherein thecapacitor dielectric layer encapsulates an upper surface, lower surface,and sidewalls of the inner capacitor electrode, and the outer capacitorelectrode has a bottom surface and outer sidewalls that make directcontact with the capacitor dielectric layer in the trench.
 3. Thesemiconductor structure of claim 1, further comprising: a doped regionlining sidewalls of the trench and a bottom surface of the trench. 4.The semiconductor structure of claim 1, further comprising: anintermediate capacitor electrode disposed in the trench between theinner capacitor electrode and the outer capacitor electrode.
 5. Thesemiconductor structure of claim 4, wherein at least one of the innercapacitor electrode or the intermediate capacitor electrode have anoutermost surface that is nearer to the backside surface of thesemiconductor substrate than an upper surface of a metal line in abackside interconnect structure nearest the backside surface of thesemiconductor substrate.
 6. The semiconductor structure of claim 5,wherein an outermost surface of the outer capacitor electrode is levelor planar with the upper surface of the metal line.
 7. The semiconductordevice of claim 1, wherein the semiconductor substrate includesmonocrystalline silicon, and the trench is spaced apart from the wellregion solely by a portion of the monocrystalline silicon.
 8. Asemiconductor structure comprising: a semiconductor substrate made ofmonocrystalline silicon that extends continuously and entirely between afrontside surface and a backside surface of the semiconductor substrate;a well region extending from the frontside surface into themonocrystalline silicon, and a semiconductor device disposed in or onthe well region on the frontside surface of the semiconductor substrate;a frontside interconnect structure disposed over the frontside surface,the frontside interconnect structure including a plurality of metallines and vias that are operably coupled to the semiconductor devicedisposed in or on the frontside surface; a first capacitor dielectriclayer extending from the backside surface into the monocrystallinesilicon and spaced apart from the well region solely by a portion of themonocrystalline silicon; a first capacitor electrode extending into thebackside surface of the semiconductor substrate and lining innersidewalls of the first capacitor dielectric layer and extending over abottom surface of the first capacitor dielectric layer; a secondcapacitor dielectric layer extending into the backside surface of thesemiconductor substrate and overlying inner sidewalls of the firstcapacitor electrode and extending over a bottom surface of the firstcapacitor electrode; and a second capacitor electrode extending into thebackside surface of the semiconductor substrate and overlying innersidewalls of the second capacitor dielectric layer and extending over abottom surface of the second capacitor dielectric layer.
 9. Thesemiconductor structure of claim 8, further comprising: a doped regiondisposed in the backside surface of the semiconductor substrate, thedoped region extending beneath the bottom surface of the first capacitordielectric layer and extending along outer sidewalls of the firstcapacitor dielectric layer.
 10. The semiconductor structure of claim 8,wherein the first capacitor electrode has a lower portion that extendsinto the backside surface of the semiconductor substrate and an upperportion that extends over the backside surface of the semiconductorsubstrate.
 11. The semiconductor structure of claim 10, wherein theupper portion extends horizontally over the backside surface of thesemiconductor substrate.
 12. The semiconductor structure of claim 11,wherein the upper portion of the first capacitor electrode extends to afirst height over the backside surface, and wherein the second capacitorelectrode has an uppermost surface that extends to a second height overthe backside surface, the second height being greater than the firstheight.
 13. The semiconductor structure of claim 8, wherein the secondcapacitor electrode has a U-shaped cross-section.
 14. The semiconductorstructure of claim 13, further comprising: a dielectric materialdisposed over the backside surface; and a metal interconnect linedisposed within the dielectric material; wherein the dielectric materialextends into an inner recess of the U-shaped cross-section of the secondcapacitor electrode.
 15. The semiconductor structure of claim 8: whereina thickness of monocrystalline silicon separates the frontside surfaceof the semiconductor substrate and a nearest point of the firstcapacitor dielectric layer, the thickness of monocrystalline siliconbeing measured in a direction perpendicular to the frontside surface ofthe semiconductor substrate; and wherein the well region extends to adepth as measured in the direction from the backside surface into themonocrystalline silicon, the depth of the well region being less thanthe thickness of monocrystalline silicon separating the frontsidesurface of the semiconductor substrate and the nearest point of thefirst capacitor dielectric layer.
 16. A semiconductor structurecomprising: a semiconductor substrate comprising monocrystalline siliconand having a frontside surface and a backside surface; a well regionextending into the frontside surface of the monocrystalline silicon; afrontside interconnect structure disposed over the frontside surface,the frontside interconnect structure including a plurality of metallines and vias that operably couple semiconductor devices disposed in oron the frontside surface of the semiconductor substrate to one another;a first capacitor dielectric layer extending into a recess in thebackside surface of the semiconductor substrate and separated from thewell region solely by a region of monocrystalline silicon of thesemiconductor substrate; a first capacitor electrode disposed over thefirst capacitor dielectric layer in the recess, the first capacitorelectrode lining inner sidewalls of the first capacitor dielectric layerand extending over a bottom inner surface of the first capacitordielectric layer; a second capacitor dielectric layer disposed over thefirst capacitor electrode in the recess, the second capacitor dielectriclayer overlying inner sidewalls of the first capacitor electrode andextending over a bottom inner surface of the first capacitor electrode;and a second capacitor electrode disposed over the second capacitordielectric layer in the recess, the second capacitor electrode overlyinginner sidewalls of the second capacitor dielectric layer and extendingover a bottom inner surface of the second capacitor dielectric layer.17. The semiconductor structure of claim 16, wherein the first capacitordielectric layer encapsulates an upper surface, the bottom innersurface, and the inner sidewalls of the first capacitor electrode, andthe second capacitor electrode has a bottom surface and outer sidewallsthat make direct contact with the second capacitor dielectric layer inthe recess.
 18. The semiconductor structure of claim 16, furthercomprising: a doped region lining inner sidewalls of the recess and abottom surface of the recess.
 19. The semiconductor structure of claim16, further comprising: a third capacitor electrode disposed in therecess between the first capacitor electrode and the second capacitorelectrode.
 20. The semiconductor structure of claim 16, wherein thesemiconductor substrate has a reduced thickness as measured from abottom surface of the recess to the frontside surface, and the reducedthickness being less than an overall thickness of the monocrystallinesilicon and being less than a depth of the well region.